Part 24 of the series ‘High-Pressure NMR Kinetics’. Part 23: .
Article first published online: 25 OCT 2004
Copyright © 1985 Verlag GmbH & Co. KGaA, Weinheim
Helvetica Chimica Acta
Volume 68, Issue 2, pages 508–521, 27 March 1985
How to Cite
Hugi, A. D., Helm, L. and Merbach, A. E. (1985), Water Exchange on Hexaaquavanadium(III): a Variable-Temperature and Variable-Pressure 17O-NMR Study at 1.4 and 4.7 Tesla. HCA, 68: 508–521. doi: 10.1002/hlca.19850680224
These results are part of the Ph. D. thesis of A. H., University of Lausanne, 1984.
- Issue published online: 25 OCT 2004
- Article first published online: 25 OCT 2004
Water exchange on hexaaquavanadium (III) has been studied as a function of temperature (255 to 413 K) and pressure (up to 250 MPa, at several temperatures) by 17O-NMR spectroscopy at 8.13 and 27.11 MHz. The samples contained V3+ (0.30–1.53 m), H+ (0.19–2.25 m) and 17O-enriched (10–20%) H2O. The trifluoromethanesulfonate was used as counter-ion, and, contrary to the previously used chloride or bromide, CF3SO is shown to be non-coordinating. The following exchange parameters were obtained: k = (5.0 ± 0.3) · 102 s−1, ΔH* = (49.4 ± 0.8) kJ mol−1, ΔS* = −(28 ± 2) JK−1 mol−1, ΔV* = −(8.9 ± 0.4) cm3 mol−1 and Δβ* = −(1.1 ± 0.3) · 10−2 cm3 mol−1 MPa−1. They are in accord with an associative interchange mechanism, Ia. These results for H2O exchange are discussed together with the available data for complex formation reactions on hexaaquavanadium(III). A semi-quantitative analysis of the bound H2O linewidth led to an estimation of the proportions of the different contributions to the relaxation mechanism in the coordinated site: the dipole-dipole interaction hardly contributes to the relaxation (less than 7%); the quadrupolar relaxation, and the scalar coupling mechanism are nearly equally efficient at low temperature (∼ 273 K), but the latter becomes more important at higher temperature (75–85% contribution at 360 K).